Apple continues to be the industry's top device maker, at least in the number of ad impressions recorded by Millennial Media for its September Mobile Mix report.

For the second quarter of 2012, Apple took home a leading 31 percent of all ad impressions (the number of times an ad is displayed). The iPhone retained its top spot among the top 20 handsets, accounting for almost 16 percent of all impressions.

Samsung captured 22 percent of all impressions to win second place among the top 15 phone makers. The company saw eight of its phones on the top 20 handset list for a combined share of 13 percent, almost double that of the first quarter. With a share of 3.5 percent, the Galaxy S grabbed third place just behind Research In Motion's BlackBerry Curve.

RIM was the third most popular device maker with a 13 percent cut of all ad impressions, followed by HTC in fourth and Motorola in fifth.

Among smartphone platforms, Android continued to soak up the lead with 46 percent of all impressions. Apple's iOS took second place with 34 percent. That left RIM's BlackBerry OS with 15 percent, Microsoft's Windows Phone with 4 percent and Nokia's Symbian with just 1 percent.

Photo by Millennial Media

The iPad, Samsung Galaxy Tab, and Amazon's Kindle Fire were the top three tablets recorded by Millennial Media and were nestled among the top 20 of all mobile devices. A full 95 percent of all tablet impressions came over Wi-Fi connections.

Finally, smartphones scored 74 percent of all ad impressions, a healthy rise from the 66 percent found in last year's second quarter. Feature phones continued their downward spiral, accounting for only 7 percent of all impressions, down from 17 percent a year ago.

Millennial Media compiles data from its mobile ad platform and records "tens of billions of monthly ad requests," according to the company.